Onion Thrips is a key insect pest of onion
and related Allium species in many parts of the world. Thrips feed
on leaves and can kill young plants, but most often their injury results
in reduced onion yields and bulb size. Problems with controlling thrips
in commercial onion fields led scientists from New York to develop
a cooperative program between entomologists and spray technologists
in which they evaluated the efficacy of different insecticides and
sprayers. The results of the sprayer study is repeated with in this
article.
The goals of this project were to maximize spray nozzles that will
maximize spray coverage on onion leaves and to determine if onion
thrips can be controlled more effectively with these nozzles. In the
2001 nozzle trials on onions, twin-jet flat fan nozzles that use forward
and rearward pointing flat fans gave good results, but they are prone
to blockage and drift at low application rates.
In the fall of 2003, two nozzle manufacturers released the Twin Cap
nozzles system. The new nozzle cap allows sprayer operators to insert
whatever size nozzle they choose into the cap, the nozzles point forwards
and backwards, thus giving two applications, one as the sprayer travels
towards the target and the other as the sprayer moves away. To ensure
the application rate remains constant (and comparable with conventional
flat fan/cone nozzles), the quantity of spray from the forward and
rear fans can be independently changed. The operator can change droplet
size via changing forward or rear nozzles. Smaller dropets stick to
leaves; therefore the potential for better deposition may be achieved.
Trials were conducted in the pesticide application laboratory at NYSAES
Geneva to consider the best combination of nozzles/pressure and application
rate with a number of nozzle tips (see table 1). The tips were inserted
into a single nozzle spray test machine with potted onion plants placed
below the spray cloud. The spray comprised a flourescent tracer and
water. Leaf samples were removed and analyzed in a florimeter to measure
deposition. Similar size onion plants were sprayed with Warrior, and
then thrips were placed on the onion sections and mortality was determined.
The results indicate that the twin-jet flat fan at 40 gpa gave the
highest deposition, both at the base of the plant (309) and in total
(2,068). The hollow cone was second best in total deposition but the
greatest amount was at the top of leaves.
The Lurmark twin cap with two TP8004E tips gave the second highest
deposition at the base of the leaves. The advantage of using a Twin
Cap is clearly shown by deposition quantity. The forward and rear
facing nozzles give improved coverage compared to the standard flat
fan. The hollow cone does, to a limited extent, provide two “hits”
to the plant since the leading and trailing edges of the cone spray
pattern hits the onion leaves. The most important relationship, however,
is whether these differences in spray deposition results in differences
in thrips mortality on the plant. More work needs to be done in this
area.
Table 1. Variation in deposition on spray
deposits on onion leaves when using different spray nozzles in a spray
chamber, 2003.
| Nozzle Description |
Volume rate, gpa |
Pressure
psi |
Travel Speed
mph |
Tracer Deposition, ng |
Top |
Middle |
Bottom |
Total |
| TXA 8004VK red ConeJet, hollow cone spray tip pointed straight
down |
|
40 |
4 |
221.1 |
131.5 |
151.2 |
503.8 |
| TP 8004E, banding red flat fan spray tip pointed straight down |
20 |
40 |
4 |
31.0 |
79.5 |
234.5 |
344.9 |
| TP 8008E banding while flat spray tip pointed straight down |
40 |
40 |
4 |
99.7 |
92.0 |
187.7 |
379.4 |
| Lurmark Twin Cap having two TP 8002E banding yellow flat fan
spray tips |
20 |
40 |
4 |
62.5 |
114.1 |
192.2 |
368.8 |
| Lurmark Twin Cap having two 8004E banding red flat fn spray
tips |
40 |
40 |
4 |
118.5 |
63.8 |
243.9 |
426.2 |
| TJ 8006E TwinJet, twin flat fan |
40 |
40 |
3 |
533.2 |
255.8 |
309.1 |
1068.1 |
| Lurmark Twin Cap having one TP8004E banding red forward facing
flat fan spray |
20 |
40 |
4 |
66.7 |
81.9 |
171.9 |
320.4 |
| Lurmark Twin Cap having one TP8004E banding red rearward facing
flat fan spray |
20 |
40 |
4 |
96.6 |
87.7 |
117.7 |
301.9 |
